In the manufacture of thin web or sheet material such as film which may be conventionally heated and stretched or otherwise heat treated utilizing tenter clips to maintain the sheet material in open width, it is necessary to exert a substantial gripping or clamping force to sufficiently secure the sheet material at its edges. Many efforts have been made to provide tenter clips having gripping shoes capable of exerting a clamping pressure over a wide area. When tentering film, the exertion of concentrated gripping action may result in penetration and tearing of the film material. An effort to reduce the possibility of surface penetration is illustrated in U.S. Pat. No. 2,708,784 wherein a vertical blade is covered at a lower edge with silicone which due to its resilient quality exerts a yielding action. Other patents illustrating a variety of tenter gripping elements include U.S. Pat. Nos. 2,232,536, 3,000,073, 3,514,823, 3,789,468 and 4,155,148.
Accordingly, it is an important object of this invention to provide a device which will present a maximum clamping surface area to minimize the clamping pressure which must be exerted by the movable jaw of a tenter clip to hold the edge of the sheet material.
Another important object of this invention is the avoidance of surface penetration resulting from stress concentration especially in thin material so that a maximum clamping force can be obtained over a wide area of the material.